Thin films measurement method and system

ABSTRACT

A method and system are presented for use in controlling the processing of a structure. First measured data is provided being indicative of at least one of the following: a thickness (d 2 ) of at least one layer (L 2 ) of the structure W in at least selected sites of the structure prior to the processing of the structure, and a surface profile of the structure prior to said processing. An optical measurement is applied to at least the selected sites of the structure after said processing and second measured data is generated being indicative of at least one of the following: a thickness of the processed structure (d′) and a surface profile of the processed structure, The second measured data is analyzed by interpreting it using the first measured data to thereby determine a thickness (d′ 1  or d′ 2 ) of at least one layer of the processed structure. This determined thickness is thus indicative of the quality of said processing.

FIELD OF THE INVENTION

This invention is generally in the field of optical measurementtechniques, and relates to a method and system for thin-film (layers)measurements. The present invention is particularly useful for processcontrol in the manufacture of semiconductor devices.

BACKGROUND OF THE INVENTION

Integrated circuits are multi-layer structures produced by applying, asequence of layer-deposition and patterning processes to a semiconductorwafer. Various steps in the manufacture of semiconductor devices requiremeasurements of thickness or other characteristics (e.g., opticalparameters) of each layer in the multi-layer wafer structure.

Optical methods for on-line or integrated measurement of the parametersof dielectric films (e.g., film thickness) are known in the art. Most ofthese techniques are based on reflectometry in a broadened spectralrange, e.g. ranging from DUV to NIR spectral range.

In order to determine the parameters of the uppermost layer in the waferstack (e.g., thickness of this layer), it is especially important todetermine optical properties of each layer (film) of the actual stackafter completing all the processing steps. Unfortunately, in cases whenmeasurements are performed on the entire stack including differentlayers that similarly affect the spectral response of the stack,accurate determination of the properties of each separate layer arealmost impossible.

SUMMARY OF THE INVENTION

There is accordingly a need in the art to facilitate measurements in amulti-layered structure, by providing a novel measuring method andsystem.

The inventors have found that performing measurements on a structureprior to applying a specific processing to the structure is advantageousand actually makes further measuring on the processed structurefeasible. A metrology system aimed at controlling a process applied tothe structure should thus be designed to be capable of using dataobtained with the pre-processing measurements to sufficiently andaccurately analyze the post-processing measurements on the samestructure.

According to one broad aspect of the present invention, there isprovided, a method for use in the controlling processing of a structure,the method comprising:

-   -   providing first measured data indicative of at least one of the        following: a thickness of at least one layer of the structure in        at least selected sites of the structure prior to said        processing of the structure, and a surface profile of the        structure prior to said processing;    -   applying optical measurements to at least said selected sites in        the structure after said processing and generating second        measured data indicative of at least one of the following: a        thickness of the processed structure and a surface profile of        the processed structure;    -   analyzing the second measured data by interpreting it using the        first measured data to thereby determine a thickness of at least        one layer of the processed structure, said determined thickness        being indicative of the quality of said processing.

There are two basic types of data obtainable with the pre-processingmeasurement: “Discrimination” and “Complementary” data. In both cases,the pre-processing measurement on the same sites with the postmeasurement plus injection of the information are key issues to enablecertain type of measurements with the required accuracy.

The first measured data is provided by applying said measurements to thestructure prior to said processing, and may present reference dataobtained while controlling a previous process applied to the structure.

According to another broad aspect of the present invention, there isprovided a method for use in controlling processing of a structure, themethod comprising:

-   -   providing first optical spectral measured data indicative of at        least one of the following: a thickness of at least one layer of        the structure in at least selected sites of the structure prior        to said processing of the structure, and a surface profile of        the structure prior to said processing;    -   applying optical spectral measurements to at least said selected        sites in the structure after said processing and generating        second measured data indicative of at least one of the        following: a thickness of the processed structure and a surface        profile of the processed structure;    -   analyzing the second measured data by interpreting it using the        first measured data to thereby determine a thickness of at least        one layer of the processed structure, said determined thickness        being indicative of the quality of said processing.

The process to be controlled may be a material removal process or alayer deposition process.

A method for use in controlling a material removal process applied to amulti-layer structure comprises:

-   -   providing first optical spectral measured data indicative of a        thickness of an uppermost layer of the structure and a thickness        of a layer underneath said uppermost layer in at least selected        sites of the structure prior to said processing of the        structure;    -   applying optical spectral measurements to at least said selected        sites of the structure after said material removal processing of        the structure, and generating second measured data indicative of        a thickness of the processed structure;    -   analyzing the second measured data by interpreting it using the        first measured data to thereby determine at least a thickness of        said underneath layer in the processed structure, said        determined thickness being indicative of the quality of said        processing.

According to one embodiment of the invention, a method for use incontrolling a layer deposition process applied to a structure comprises:

-   -   providing first optical spectral measured data indicative of a        thickness of a first layer of said structure onto which a second        layer is to be deposited;    -   applying optical spectral measurements to at least selected        sites in the structure after said layer deposition processing of        the structure, and generating second measured data indicative of        a thickness of the processed structure;    -   analyzing the second measured data by interpreting it using the        first measured data to thereby determine a thickness of the        deposited layer.

According to another embodiment of the invention, a method for use incontrolling a layer deposition process applied to a patterned layer of astructure comprises:

-   -   providing first optical spectral measured data indicative of a        surface profile of said patterned layer of the structure onto        which a second layer is to be deposited;    -   applying optical spectral measurements to at least selected        sites in the structure after said layer deposition processing of        the structure, and generating second measured data indicative of        a surface profile of the processed structure;    -   analyzing the second measured data by interpreting it using the        first measured data to thereby determine a thickness of the        deposited layer.

According to yet another aspect of the invention, there is provided anoptical system for use in controlling processing of a multi-layerstructure, the system comprising:

-   -   an optical device comprising a light source arrangement, a light        detector assembly, and a light directing assembly, the optical        device being operable to apply optical measurements to the        structure and generate data representative of light returned        from the structure, said generated data being indicative of at        least one of the following: a thickness of at least one layer of        the structure, and a surface profile of the structure;    -   a control unit connectable to the optical device to operate said        device and receive said generated data, said control unit having        a memory utility for storing first measured data obtained from        optical measurements applied to the structure prior to said        processing, and having a processor utility preprogrammed to        analyze second measured data obtained from the optical        measurements applied to the structure after said processing,        said analyzing of the second measured data including        interpreting the second measured data using the first measured        data to thereby determine a thickness of at least one layer of        the processed structure, said determined thickness being        indicative of the quality of said processing.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carriedout in practice, a preferred embodiment will now be described, by way ofnon-limiting example only, with reference to the accompanying drawings,in which:

FIG. 1 is a schematic illustration of a system according to theinvention for use in controlling processing of a multi-layer structure,such as a semiconductor wafer;

FIG. 2 exemplifies the construction of an optical device in the systemof FIG. 1;

FIGS. 3A and 3B illustrate one possible example of a process to becontrolled by the technique of the present invention;

FIG. 4 presents a one-dimensional Merit Function (MF) plot, as MF vs.layer thickness in the structure of FIGS. 3A-3B;

FIG. 5 illustrates a block diagram of a method according to theinvention;

FIG. 6 exemplifies the operational steps of a processor utility of thesystem according to the invention while processing and analyzing thefirst and second measured data obtained with respectively pre-processand after-process measurements; and

FIGS. 7A and 7B illustrate another example of a process to be controlledby the technique of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is schematically illustrated a system 10 ofthe present invention for controlling the processing of a multi-layerstructure (e.g., semiconductor wafer) W by a processing tool 15A of aprocessing system 15. The system 10 comprises such main constructionalparts as a measuring device (e.g., optical device) 12 and a control unit14 connectable thereto. The control unit 14 is a computer systemincluding inter alia a memory utility 14A and a data processing andanalyzing utility 14B.

As shown in the specific but non-limiting example of FIG. 1, the system10 is of the integrated type, is accommodated within the processingsystem 15 in the vicinity of the processing tool 15A, but outside theprocessing area defined by this tool. The control unit 14 is connectableto the processing tool (either directly or via a control unit of theprocessing system that operates this processing tool), and operates foranalyzing measured data coming from the optical device 12 and generatingan output indicative of the data analysis results to be used inoperating the processing tool. The operation of the system 10 and itscontrol unit 14 will be described further below.

The construction and operation of the optical device 12 do not form partof the present invention, and, generally, this device may be of anysuitable design capable of providing accurate layer thicknessmeasurements or topological profile measurements of a multi-layerstructure. For example, the optical device may utilizespectrophotometric and imaging channels.

One specific but non-limiting example of such an optical device is thatdisclosed in U.S. Pat. No. 6,045,433, assigned to the assignee of thepresent application. This device implementation is schematicallyillustrated in FIG. 2. In this specific example, the optical device 12utilizes a microscope-based spectrophotometer. The device comprises alight source arrangement 16, including a light emitting unit 16A and acondenser 16B; a detector assembly including a spectrophotometer 20Awith its associated imaging optics 30A (e.g., relay lens) and an imagingdetector 20B (e.g., CCD camera) with its associated imaging optics 30B(e.g., relay lens); and a light directing assembly 18. The latterdefines spectrophotometric and imaging light propagation channels, andcomprises a lens arrangement formed by an objective lens 22 and afocusing lens 24; a beam splitter 26; and a pinhole mirror 28.

Light from the light source 16A is provided (e.g., along an opticalfiber) to the condenser 16B, which directs the light towards the beamsplitter 26. The latter directs the light towards the wafer surface Wvia lenses 24 and 22.

Light returned (reflected or scattered) from the wafer is collected byobjective 22 and focused by lens 24 onto the pinhole mirror 28. Aportion of this light impinging onto the pinhole mirror 28 passesthrough the hole in this mirror and is focused by the relay lens 30Aonto the spectrophotometer 20A. The other portion of light impingingonto the pinhole mirror 28 is reflected therefrom towards the relay lens30B that focuses this light onto the CCD camera 20B. Since the pinholeis placed at the center of the image plane, which is the focal plane ofthe lens 24, it acts as an aperture stop, allowing only the collimatedportion of the light beam to pass through. Thus, the pinhole drasticallyreduces any scattered light in the system. Relay lens 30A collects thelight from the pinhole and provides it to spectrophotometer 20A.Furthermore, since the pinhole is located at the image plane of theoptical imaging system (lenses 22 and 24), only that portion of thelight, reflected from the wafer's surface, which is the size of thepinhole divided by the magnification will come through the pinhole.Relay lens 30B collects this light and focuses it onto the CCD camera20B. The pinhole serves to locate the measurement spot in the image ofthe wafer. Since the pinhole allows light to pass through it, ratherthan being reflected toward the CCD camera 20B, the pinhole appears as asharp dark point in the image produced by the lens 30B. Thus, whenviewing the CCD image, the location of the measurement spot isimmediately known, it being the location of the dark spot.

FIGS. 3A and 3B schematically illustrate one example of a process to becontrolled while manufacturing multi-layer structures, such assemiconductor wafers. In this example, a wafer W is partly shown priorto and after a material removal process (polishing, e.g., CMP). In thisspecific example, monitoring STI (shallow trench isolation) isconsidered, and the wafer W includes three layers—Silicone Oxide (SiO₂)layer L₁, Silicon Nitride (Si₃N₄) layer L₂ and Si layer L₃. Theprocessing consists in removing the uppermost layer material L₁ from theupper surface of layer L₂. As shown in FIG. 3B, the processed wafer Wmay have a thin layer of SiO₂ residuals.

The process control in this case is aimed at determining the existenceof residuals of the layer material L₁ and/or the thickness of theremaining Silicon Nitride (Si₃N₄) layer L₂. To this end, the thicknessof the layers L₁ and L₂ is to be measured after the polishing iscomplete, or is to be periodically or continuously measured during thepolishing (in-situ), as the case may be.

The standard approach for controlling the process of layer L₁ removalconsists of performing only post-polishing (or in-polishing)spectrophotometric measurements, and analyzing the so-obtained measuredspectrum to understand the two thickness values d′₁ and d′₂ of,respectively, the Silicon Oxide layer L₁ residues and the SiliconNitride layer L₂ forming (total) processed structure with thickness d′.The data analysis is based on data interpretation for both the SiliconNitride layer and the Silicon Oxide residues via Merit Function (MF)calculation for regression fit.

It appears that the standard post-polishing spectrophotometricmeasurement is complicated and practically impossible in the case wherethe thickness of layer L₁ is too small and/or the layers L₁ and L₂ havevery similar optical properties with respect to incident radiation usedin optical measurements. Practically, the standard approach is incapableof distinguishing the layer of Silicone Oxide of less than 100 thicknessfrom the underneath Silicon Nitride layer. In a typical example, thewafer stack after polishing includes OA Silicon Oxide layer L₁, 970 ÅSilicon Nitride layer L₂ and a lower 80 Å Pad Oxide/Si layer L₃. Thelimitation in this case comes from the fact that the basicdiscrimination of each of these transparent layers is proportional to aproduct (n·d), wherein n is the refraction index of the respectivelayer. So, measuring (n₁·d+n₂·d₂) for d₂<<d₁ is problematic, as long asthese parameters satisfy the following relation:

n ₂ ·d ₂<<(n ₁ ·d ₁ +n ₂ d ₂)

The rate of MF change vs. thickness change for each material presentsthe sensitivity of the regression fit to this parameter. It appears thatthere is no sensitivity to small Silicon Oxide thickness, while for theSilicon Nitride thickness, the rate of change is much sharper.

The present invention solves the above problem by utilizing dataindicative of optical measurement results on the wafer W prior to beprocessed (pre-process measurement) for the analysis of an after-processmeasurement. This pre-process measured data can be provided either byapplying optical measurements to a wafer arrived for the specificprocessing, or by utilizing after-process measured data associated witha prior manufacturing step. In this specific example of material removalof layer L₁, such a pre-process measurement may be that obtained aftercompleting the deposition of this layer L₁, for example, previouslyobtained for the purposes of controlling the deposition process.

As indicated above, the post-polishing measurement of (n₁·d₁+n₂·d₂) ford₂<<d₁ is problematic as long as n₂·d₂<<(n₁·d₁+n₂·d₂). This condition,however, is not valid for a pre-polishing state (or after-depositionstate), and this measurement can be accurately executed using theinterpretation of both parameters simultaneously, since each layerthickness significantly affects the measured spectrum. For a typicalsituation of the stack comprising 4840 Å Silicon Oxide layer L₁, 960 ÅSilicon Nitride layer L₂ and 80 Å STI Pad Oxide/Si layer L₃, the MFslopes for the thicknesses of layers L₁ (Oxide) and L₂ (Nitride) aresignificantly high, thus ensuring good convergence sensitivity for bothparameters. The mutual effect of one thickness on the other thickness isminor and good accuracy can be achieved even for simultaneous datainterpretations. Hence, according to the technique of the presentinvention, data indicative of thicknesses d₁ and d₂ of layers L₁ and L₂,respectively, are determined in the pre-polishing state of the wafer W,and then data indicative of thickness d₂ is “injected” to theinterpretation of the post-polishing measurement.

FIG. 4 presents a one-dimensional MF plot, namely, MF vs. Silicon Oxidethickness (layer L₁ in FIG. 3). The minimum of this function at zerothickness is well defined. The Nitride layer thickness d′₂ at theafter-polishing state of the wafer can be easily and accuratelyinterpreted using optical measurements at the pre-polishing state of thewafer. By this, ambiguity regarding small errors in the Silicon Nitridethickness and large errors in the Silicon Oxide thickness can beavoided.

Turning back to FIG. 1 and referring to FIG. 5 illustrating a blockdiagram of a method according to the invention, the system 10 accordingto the invention operates in the following manner.

Measured data MD₁ (constituting first measured data), obtained byapplying optical measurements to the wafer W prior to be processed bythe tool 15A, is provided (Step I). The first pre-process measured dataMD₁, is indicative of thicknesses d₁ and d₂ of layers L₁ and L₂,respectively.

This data MD₁ may be obtained while controlling a previous manufacturingprocess of depositing layer L₁ onto layer L₂ (e.g., CVD process). Inthis case, measured data MD₁, for controlling the polishing process,presents reference data previously supplied to the control unit 14 andstored in its memory utility 14A. Alternatively, or additionally, thefirst measured data MD₁ is obtained when the wafer W arrives to thepolishing system 15. In this case, considering the integratedimplementation of the system 10 (e.g., utilizing the same wafer transfermeans of the processing system 15), the wafer W to be processed by theprocessing tool 15A is first supplied to a measurement area defined bythe optical device 12. The control unit 14 operates the optical device12 to apply optical measurements to at least selected sites of the waferW and generate first measured data MD₁ indicative of the thicknesses d₁and d₂ of layers L₁ and L₂, respectively. This measured data MD isreceived at the control unit 14 and stored in the memory utility 14A.

The processed (polished) wafer W is supplied to the measurement areadefined by the optical device 12. The control unit 14 operates theoptical device 12 to apply a post-process optical measurement andgenerate second measured data MD₂ (Step II). This second measured dataMD₂ is indicative of a thickness d′ of a structure after processing,including thickness d₂′ of layer L₂ and layer material L₁ with thicknessd₁′ that might remain on top of layer L₂. The control unit 14 analyzesthe first and second measured data to discriminate between opticalparameters that have non-orthogonal contribution to the opticalmeasurement and determine at least the thickness d₂′ of layer L₂ in theprocessed wafer (Step III). Since the thickness of layer L₂ has not beenaffected by the polishing and therefore remains the same as in thepre-process state of the wafer, the so-obtained data indicative of thethickness of layer L₂ in the processed wafer is indicative of thethickness d₁′ of layer material L₁ on top of layer L₂ in thepost-process wafer state, and is thus indicative of the quality ofpolishing, namely, whether the working parameters of the polishing toolare to be corrected or not. The control unit 14 thus generates a controlsignal indicative of the data analysis results to be used in operatingthe processing tool accordingly.

FIG. 6 exemplifies the operational steps of the processor utility (14Bin FIG. 1) while processing and analyzing the first and second measureddata MD₁ and MD₂. In this specific example, the polishing is aimed atcomplete removal of layer L₁ and partial removal of layer L₂. Forexample, the case may be such that material L₁ is deposited on thepatterned surface of layer L₂ to fill grooves in layer L₂. As indicatedabove, first measured data MD₁ is not necessarily obtained just prior toapplying to the wafer a specific process to be controlled. In the caseof controlling a polishing process, first pre-processed measured dataMD₁ might be that obtained during the control of a previous CVD processapplied to the same wafer, and thus the pre-process measured data MD₁for polishing process presents a post-process measured data for thedeposition process. Second measured data MD₂ is that obtained fromoptical measurements applied to at least selected sites of the polishedwafer, provided these sites have been measured in a pre-polished stateof the wafer. With regard to the post-polishing measurement, it isassumed that there is no layer L₁ on top of layer L₂, and thus data MD₂indicative of the thickness value d′ obtained in the post-polishingmeasurement is to be compared to data MD₁ indicative of the layer L₂thickness d′₂ at the pre-polished state of the wafer.

The processor utility thus identifies whether data MD₁ and MD₂ areindicative of that thickness d′ at the post-polish state is below thepre-polished thickness d₂ or not. To this end, a certain predeterminedthreshold is considered defined by an acceptable error for thepre-polishing measurement (about 5 Å). If d′ is smaller than d₂, thedifference between d′ and d₂ is interpreted using a one-dimensionalfunction of MF vs. Nitride thickness, thereby enabling the determinationof thickness d′₂ in the polished wafer, i.e., the measurement isfinished by presenting the Silicon Nitride actual thickness result d′₂and zero Silicon Oxide thickness residual d′₁ (i.e. no residuals). Ifthe measured thickness d′ is equal or higher than d₂ of the pre-polishedwafer, the second measured data is interpreted for the Silicon Oxidelayer with the known pre-polishing Silicon Nitride thickness d₂, therebyenabling the determination of both Nitride and Oxide layers' thicknessesd′₁ and d′₂ in the post-polished wafer.

The above technique of the present invention can advantageously be usedfor controlling a Physical Vapor Deposition process (PVD) of thin metalfilms. In this case, the measurement on a structure in a pre-processstate could provide data that otherwise, due to measurement limitations,cannot be measured by the standard techniques. Such a pre-processmeasurement could provide a set of starting condition for a furthermeasurement (e.g., thickness of underlying layers) to improve theinterpretation of the further measurement. A typical example of thisapplication is measuring in multi stacks of thin metals layers usingoptical methods. By additions of metal deposition steps, the metal stacklayers can become practically opaque. Therefore, measuring in thin metallayers prior to an additional layer deposition step enables to achievebetter accuracy measurement, and may actually determine the need forsuch type of measurements. Simultaneous layer thickness measurements ina structure formed by two thin metal layers might be impeded by errorcontribution from one metal to the other metal (due to diffusion effectsat the interface between these layers). An example of such a structureis that formed by Tungsten (W) and Tungsten Nitride (WN) films, wherethe mutual contribution from W film to WN film is of the level of a fewangstroms. The present invention provides for eliminating any additionalcontributions and having better repeatability for each of the layerthickness measurements in the W/WN stack by measuring the metal layerthickness after each deposition layer deposition process and utilizingthese measurement results to control the deposition of a further layer.For example, the calculation has shown an improvement in therepeatability from 2.5 Å to 1.1 Å for the upper layer.

Reference is now made to FIGS. 7A and 7B, illustrating yet anotherexample of a process to be controlled while manufacturing multi-layerstructures, such as semiconductor wafers. In this example, a wafer W isshown prior to and after a material L₁ deposition process (e.g.,Sputtering or CVD) onto a patterned surface of layer L₂ having trenches,holes, etc. The technique of the present invention provides foradvantageously controlling this material deposition process by providingmeasured data from the preprocessed wafer (FIG. 7A) and utilizing thispre-deposition measured data for interpreting measured data from thepost-processed wafer (FIG. 7B). The measurements are preferably based onscatterometry.

In that case, the basic sensitive capability is the measurement of shapeof features (topological profile) covered by metal deposition. Thescatterometry technique could not resolve with the required accuracy,parameters of metal thickness (for layers thicker than few hundredsangstroms), and especially the thickness of the metal layer covering thesidewalls. However, its sensitivity to shape parameters such as trenchslopes, trench depth, trench opening (CD top), is extremely higher. Inthis case, these shape parameters could be measured with very goodrepeatability and accuracy.

More specific is the case of the barrier and seed layers deposition stepthat is a preliminary step for electroplating in the Damascene process.Each metal deposition process is a stage for a shape measurement basedon the very sensitive parameters. Accurate and repeatable measurementson the same site prior and after each deposition step can yielddifferent shapes, whose subtraction presents an actual thickness of thelayer that has been deposited in this process step.

The present invention may be used for controlling various depositionsteps by measuring layers' parameters (e.g., thickness) prior to andafter the deposition. The structure profile (shape) is measured prior tothe barrier layer L₁ deposition on the structure, and the first measureddata (profile) indicative of this pre-deposition measurement isgenerated. After completing the barrier layer deposition process, ameasurement of the structure profile in the same measurement site isperformed, and second measured data indicative of the post-depositionstructure profile is generated. The actual thickness of the depositedlayer is calculated as a difference between the second and firstprofiles. It should be noted, that actually the first measurement(constituting a pre-process measurement for the deposition process)could be performed after completing the step of trench etching, e.g.,using a measurement system integrated with the etcher tools arrangement.The second measurement, constituting the post-deposition measurement forone layer, could be performed as a pre-process measurement for the seedlayer deposition process. A similar technique could be applied for thecontrol of the seed layer deposition process. In that case, the firstmeasurement is performed prior to the seed deposition step (or afterbarrier layer deposition) and the second step is performed aftercompleting the seed layer deposition (or prior to step ofelectroplating).

Process control for electroplating providing information on the metallayer thickness in all direction sidewalls, and bottom of the trenchalso could be provided in accordance with the present invention. In thatcase, the first measurement is performed prior to the electroplatingstep (or after seed layer deposition) and the second step is performedafter completing the step of electroplating (or prior to the step ofpolishing or photolithography). Such process control for electroplatingenables to eliminate or at least significantly reduce void ornon-sufficient coverage problems.

The Table presented below illustrates the analysis of such capabilityfor pre- and post-seed layer deposition measurement. Presented is acalculation that was done using repeatability data retrieved from anoptical scatterometry tool that gives data for the CD top and sidewallslopes of the trench that was covered with a metal layer. In thiscalculation, the maximal error that can be caused by the subtraction oftwo shapes (pre-seed and post-seed deposition) measured by scatterometryis analyzed.

Error of pre- process + post- process Measurement in measurementpost-process state Seed with Measurement of for known pre- measuredpre-processing process profile barrier error SEED for known problemsBarrier error barrier profile 0.288 0.144 0.144 Contribution ofreference point error “CD top” - STDEV[nm] 1.903 0.951 0.951 Error dueto slope contribution - STDEV[nm] 2.191 1.095 1.095 Worse error for anypoint across profile - STDEV[nm] 8.15% 4.08% 4.08% Worse error for anypoint across profile - STDEV [% of seed thickness]

Thus, the present invention can advantageously be used for controllingthe processing a multi-layer structure, such as a semiconductor wafer.The process to be controlled may be a layer deposition or layer removalprocess. The measurements preferably utilize optical means but,generally, any other kind of measurements can be used, provided they arecapable of providing data indicative of thickness and/or surface profileof a structure under measurements.

Those skilled in the art will readily appreciate that many modificationsand changes may be applied to the invention as hereinbefore exemplifiedwithout departing from its scope, as defined in and by the appendedclaims.

1-17. (canceled)
 18. A method for use in controlling processing of astructure, the method comprising: providing first measured dataincluding at least one of the following parameters: a thickness of atleast one layer of the structure in at least selected sites of thestructure prior to said processing of the structure, and a surfaceprofile of the structure prior to said processing; applying spectraloptical measurement to at least said selected sites in the structureafter said processing and generating second measured data indicative ofa spectral response of at least said selected sites of the processedstructure; analyzing the second measured data using the first measureddata, and outputting data comprising a thickness of at least one layerof the processed structure, said output data being indicative of thequality of said processing.
 19. The method of claim 18, wherein saidfirst measured data is provided by applying measurement to the structureprior to said processing.
 20. The method of claim 18, wherein said firstmeasured data is reference data obtained while controlling a previousprocessing of said structure.
 21. The method of claim 18, for use incontrolling the process of material removal from the structure.
 22. Themethod of claim 21, wherein said first measured data is indicative ofthe thickness of an uppermost layer and the thickness of a layerunderneath said uppermost layer of said structure, prior to applying thematerial removal process to said structure.
 23. The method of claim 22,wherein said process to be controlled is aimed at removing the uppermostlayer and partially removing the underneath layer.
 24. The method ofclaim 22, wherein said output data includes a thickness of saidunderneath layer of the structure.
 25. The method of claim 22, whereinsaid output data includes a thickness of said underneath layer and athickness of said uppermost layer of the structure.
 26. The method ofclaim 22, wherein said first measured data is provided by applyingmeasurement to the structure after the uppermost layer depositionprocess.
 27. The method of claim 18, for use in controlling the processof depositing an upper thin layer onto a lower thin layer of thestructure, wherein the upper and lower layers materials are of the kindcapable of diffusing one into the other within an interface regionbetween the layers.
 28. The method of claim 27, wherein said firstmeasured data is indicative of the thickness of said lower layer, andsaid output data comprises a thickness of the upper layer.
 29. Themethod of claim 18, for use in controlling the process of depositing anupper layer onto a patterned surface of a lower layer, the firstmeasured data being indicative of the surface profile of the patternedlower layer, said output data comprising a thickness of the depositedlayer.
 30. An optical system for use in controlling processing of amulti-layer structure, the system comprising: an optical devicecomprising a light source arrangement, a light detector assembly, and alight directing assembly, the optical device being operable to applyoptical measurement to the structure and generate measured datarepresentative of light returned from the structure, said generatedmeasured data being indicative of at least one of the following: athickness of at least one layer of the structure, and a surface profileof the structure; a control unit configured to operate said device toapply the optical measurement to the structure before and after saidprocessing, and to receive data generated by the optical device, saidcontrol unit having a memory utility for storing first measured datagenerated by the optical device when applied to the structure prior tosaid processing, and having a processor utility preprogrammed to analyzesecond measured data generated by the optical device when applied to thestructure after said processing, said analyzing of the second measureddata including interpreting the second measured data using the firstmeasured data and outputting data comprising a thickness of at least onelayer of the processed structure, said output data being indicative ofthe quality of said processing.